Playing over your own games and master games is excellent for improving.
My own method of study... which, correct or not, has brought me up to 2350 chess.com Daily dating... consists of:
Play Rapid or Daily time-controls to get better, play Blitz or Bullet to have fun. Blitz and Bullet are for fun, not for chess improvement. You cannot improve if you don't take time to think.
Review every one of your lost games, and try to figure out WHY you lost it. DO NOT just ask the computer to look over the game. The computer already KNOWS how to play chess. We are trying to teach YOU, not the computer. Look over the game with your own eyes and mind. Try to find the major errors yourself.
People commonly misuse the Game Review or Analysis feature. Generally speaking, there is very little point in finding out what specific move you should have made in some specific position that will probably never occur again in your games. The important info that you should be learning from game reviews is how to look at a new position, what questions you should be asking yourself, what features of the position you should be paying attention to.
Don't bother studying opening variations. A large number of the lower-ranked players on this website have fallen into the Memorization trap... believing that they can improve their play by memorizing hundreds of move sequences. Naturally, this doesn't improve their PLAY at all. It might improve their rating a bit, but the only way to improve your PLAY is by increasing your understanding of the game. Memorization will not do that, and will leave you hanging as soon as the opponent goes out of your "book" lines.
The proper way to learn an opening is by studying complete Master games played in that particular opening. Choose a chess Master who often plays the opening that interests you (Botvinnik or Uhlmann for the French Defense, for example, or Fischer or MVL for the Najdorf), collect some of their games in that opening, and play through the games from move one right to the end. That way you learn not just a bare sequence of moves, but also the typical opening patterns, middle-game formations, plans, strategies, tactics and even endgames that are associated with the opening you've chosen to study.
Regarding "stuck at 1600":
I used to teach chess at chess clubs, and I found that when my students learned some new concepts... especially strategic rather than tactical concepts... their results and their rating would often go down instead of up, as they struggled to assimilate the new knowledge into their playing style and make it part of their usual technique.
Only after they had succeeded in "digesting" the new ideas would their results and their rating shoot up to a new high.
So recently I've been stuck at 1600 and can't get higher than 1600. So now its been like 2-4 weeks that I'm stubbornly training, going to chess lessons, doing puzzles, analyzing many grandmaster chess games (and my games too) But still there is not that much of a results, just only slight increasment of confidence. Can anybody tell me what to do and what not to do and how to improve? Thanks!